A conventional metal-semiconductor transistor utilizing GaAs (simply called "GaAsMESFET" hereinafter) is generally fabricated on a GaAs semiconductor substrate. Instead of such a GaAsMESFET, a GaAsMESFET fabricated on a Si semiconductor substrate has been proposed in the report entitled "Metal-semiconductor field-effect transistors fabricated in GaAs layers grown directly on Si substrates by molecular beam epitaxy" by G. M. Metze et al on pages 1107 to 1109 of "Applied Physics Letters 45(10), 15 November 1984." The GaAsMESFET comprises a semi-insulating Si substrate, an amorphous GaAs layer grown on the semi-insulating Si substrate, an undoped GaAs layer grown on the amorphous GaAs layer, an n-GaAs layer grown on the undoped GaAs layer, and gate, source and drain electrodes respectively provided on the n-GaAs layer. The GaAsMESFET is not described in detail herein because it is described in detail in the above mentioned report.
In addition, it is expected that an optoelectronics device will have expanded uses in an optical communication system, local area network (LAN), data link system and so on in accordance with the progress of optical communication technology. In order to adapt an optical device to a high performance optical system, the optical device is required to be of high performance, and so on. The optoelectronics device should have not only such advantages as a low fabrication cost, compact size, high reliability, non-adjustment quality and so on in accordance with the integration thereof, but also to be improved in regard to its response and sensitivity, thereby making it applicable to such a prospective optical communication system as an optical interconnection system, optical switching system and so on.
For this purpose, an optical device utilizing InP system material has been put into practical use in the field of optical communication for the reason that the optical device can be operated with high reliability, good matching property in a low loss and low dispersion wavelength band for an optical fiber and so on in accordance with the characteristics of the material.
In an electronics device utilizing such a InP system semiconductor material, it is difficult to obtain Schottky contact. A metal-insulator film semiconductor field-effect transistor (MISFET), junction gate field-effect transistor (JFET), and heterostructure junction bipolar transistor (HBT) have been researched and developed. A MISFET, on the other hand, is disadvantageous in that drift is high due to the surface state thereof. In the JFET and HBT the construction and fabricating process thereof are complicated, and the integration together with an optical device is difficult to be performed, although the operation thereof is stabilized.
On the contrary, an appropriate property of Schottky contacts can be obtained in the MESFET utilizing GaAs system semiconductor so that integrated circuits (IC's) will be shortly put into practical use in a class of large scale integrated circuits (LSI's) in accordance with the progress of FET integrating-process technology. In an optical device, on the other hand, disadvantages including decreased reliability in an optical device, and a limited transmitting property dependent on a transmitting loss and wavelength dispersion of an optical fiber result.
In order to compensate for the different disadvantages of InP and GaAs system materials, there is a study in which the optimum combination of InP system material for an optical device and GaAs system material for an electronics device is being sought for an optoelectronics integrated circuit utilizing a composite material of InP and GaAs systems. In this respect, an optoelectronics monolithic integrated device, in which a photoreceiver consisting of GaInAs to be associated with a MESFET consisting of GaAs provided on a semi-insulating GaAs substrate in accordance with the growth of GaInAs by a strained heteroepitaxy in a low pressure metalorganic chemical vapor deposition, has been proposed in the report entitled "Planar monolithic integrated photoreceiver for 1.3-1.55 .mu.m wavelength applications using GaInAs-GaAs heteroepitaxies" by M. Razeghi on pages 215 to 217 of "Applied Physics Letters 49 (4), 28 July 1986".
According to the conventional GaAsMESFET as described before, however, there is a disadvantage that a field-effect transistor is formed with difficulty on the InP substrate due to the mismatching of lattices. For this reason, the GaAsMESFET is fabricated separately from such an optical device as a laser etc. which is formed on the InP substrate. Thereafter, the MESFET is connected through wirings to the optical device to form a driver for the optical device or an amplifier for a photoreceiver, however, with this arrangement, energy loss and noise are increased due to the presence of the wirings, and the whole configuration becomes enlarged due to the separate fabrications thereof. Additionally, an electronics device such as a logic circuit is not easily formed on the InP substrate.
According to the optoelectronics monolithic integrated device as described before, there are the further disadvantages that appropriate properties of an optical device are not obtained in an optical communication system, and reliability thereof is extremely decreased due to the dislocations caused by the mismatching of lattices because an optical device of a minority carrier device is formed on a semi-insulating GaAs substrate by a strained heteroepitaxy.